1. Field of the Invention
The present invention relates to a pulse discharge lamp, and more particularly to an electronic flash tube which includes a substantially cylindrical discharge tube having an anode (or cathode) electrode mounted at each end thereof on a lead through pin, and which includes an ignition electrode carried on the external surface of the tube in the form of a longitudinal wire, strip coating, transparent coating, or the like, the ignition electrode extending substantially along the interval between the anode (cathode) electrodes, i.e. over the discharge interval.
2. Description of the Prior Art
Those skilled in the art will appreciate that ignition difficulties occur in discharge lamps of the type mentioned above, which ignition difficulties are caused, among other things, by static charging of the vessel wall and by very long drift discharge distances.
In the past attempts have been made to overcome these difficulties by applying the particular electrode potential to the surrounding discharge vessel wall, thus avoiding disturbances due to charge phenomena. To this end, for example, one electrode space is provided with a coating of barium or the like extending at least up to the end of the ignition electrode, by the use of a gettering substance. Another solution involves the formation of the electrodes in such a fashion that their external periphery is directly touching the vessel wall.
The techniques employed heretofore, and described above, are technically unsatisfactory in the manufacture of discharge tubes, and in particular in the production of pulse discharge lamps because, for example, when carrying out gettering, the formation of the metal mirror is an uncontrolled process, and its cohesion and conductivity are impaired when degasing of the relevant electrodes takes place. The introduction and melting in of large area electrodes touching the vessel wall, however, involves difficulties in manufacture because the electrodes generally must be introduced into tubes of material having a high melting point, and in doing so are sometimes so highly heated that stress cracks or other modifications occur in the vessel wall. Also, the risk of breakage in such arrangements, with electrodes which are in a peripheral contact arrangement, is substantially higher than in other forms.